Tehachapi, BC

[Scottl]

I'm not sure if this helps.  I am contemplating the same thing for my rock sheds and tunnel portals and was contemplating making my forms much as you have shown with styrene or wood strip.  On the suggestion of someone here I bought some resin detail sheets with the concrete wall cast marks and they are much finer and more realistic than I can make from parts.  As of yesterday, I have successfully used them as masters to pour plaster for wallls, my next step is to build up some sidewalls to pour the correct shape for the tunnel portal, etc.  The detail sheet has the same texture as the sample Ed gave you with a subtle irregularity and concrete texture.

I sprayed the resin detail sheet with a mold release before applying the plaster of Paris and it came off cleanly with no plaster residue.

Just some thoughts.  The Shapeways forms are very nice but the texture will be rather uniform up close.

[GaryHinshaw]

On the suggestion of someone here I bought some resin detail sheets with the concrete wall cast marks and they are much finer and more realistic than I can make from parts.

Could you elaborate Scott? That sounds perfect.

[Scottl]

Not enough caffeine to remember it this morning...

The resin boards are made by Fine N Scale, http://www.finenscale.com/architectural.html Part FNA 3603. The detail in these castings is excellent:  subtle but very convincing.  As soon as I had them in hand I knew I could not do better myself.

I bought them from MBK a few months ago but I see they are currently not listed.  For the cast, I used Ease-release which is a spray on silicon-based mold release and the plaster came clean off the resin after curing.  I don't know if it is actually needed, but I did not want to risk damaging the master.

I've cut some narrow strips of the board material for the sides and my next experiment is to cast a portal/wing wall all at once.  I need to figure out how to degas the plaster as I had a few bubbles.

[davefoxx]

If it were me, I'd consider anchoring cement for those tunnel liners, since they're short.

DFF

[Cajonpassfan]

Yea, that's a challenge. Photo decals?
As to casting larger plaster objects, I've used round toothpicks and even thin bamboo skewers cut into sections for rebar...
Otto

[Scottl]

Good idea about the rebar...

[GaryHinshaw]

DFF, good idea about the anchor cement.  I'll add that to the shopping list.  Thx.

Otto, a printed photo for the flat portal face might work really well here.  hmm...

Scott, did you use the wall as a mould, or as a master for a mould?  I gather the former.   Added - Is part no. FNA-3603 the piece you're referring to?

[Scottl]

That is the correct part.  I bought three and have found it gives me plenty to work with. 

I used it for a mold, although I have contemplated making a master from it. It is a stinky and unpleasant resin to work with and form, so my current preference is to build up a mold for each portal, with the complete wall sheet as the bottom, and scaled sidewalls I cut from another wall sheet of the resin or styrene for the rounded part of the portal opening.  If I get a really good casting, I might make a silicon rubber mold, but I wonder if it is worth the trouble and materials.

In my test yesterday, after I poured the plaster into this mold I topped it with another sheet of the wall material so that the plaster cast would have wood form marks on all sides.  Aside from some bubbles, it worked very well with minimal flash.  I assembled it all with clay backing to support the side walls and prevent leaks and it is all reusable.  I have a low vacuum system that I may try it with next time.

Thinking about the anchor cement, I prefer the plaster because of the set time and the base white color, which can be weathered to my prototype much easier than the gray of the anchor cement.  I tried to use leveling cement which is a nice light brown color when cured (and I have a spare 45 lb of  ) but it needs to be sieved to remove the sand in it.  It also takes a long time to cure, which means more chances of problems with my makeshift mold.

[ednadolski]

Hey Gary, glad to see those masters have come in handy     For painting and weathering the plaster portals, check out these couple of posts from a while back:

https://www.therailwire.net/forum/index.php?topic=18458.msg163010#msg163010
https://www.therailwire.net/forum/index.php?topic=18458.msg163045#msg163045

Those were HO scale, but I am planning to do similar for my N-scale work.

The printed portals seem interesting, and likely would save some work (with the tradeoff of some coin).  However I really like what you've done with the castings, esp. in that last pic.   JMHO the printed portals do have a nearly 'perfect' look to them, but the portals in the Pass in the era you are modeling are nearly 100 years old.   With plaster I can chip and distress it with an X-acto blade or sharp awl, to simulate the areas on the prototype where the concrete has crumbled and chipped away over the years, like in this picture:
 


If you are interested in the tunnel interiors, here is one of the most detailed pics I could find online:

http://hewgill.com/photo/trips/tehachapi-loop/IMG_5432.JPG

If you are going to cast interiors then I think the anchor bolt cement should work as good as plaster (just be sure to leave yourself with a way to remove the inner forms... they won't just 'slide' out )   The cement may be a little harder to chip/distress as above, and I am not sure how well it takes & holds paint.   One other thought: if you use cast interiors with the printed portals, that could leave you with tunnels that actually have more texture & detail on the interior than on the exterior

Ed

[GaryHinshaw]

Thanks gents.  Ed - I was going to hunt down your threads, so thanks for posting the links and saving me the time.   Completely agree about the spalling being a key spotting feature.  That is the #1 reason to stick with cast plaster over photos or Shapeways. 

I had that Tunnel 10 web page book-marked already.   And my Tunnel 10/14 hybrid will be the easiest one to see through, so it is a key detail to get right.  After all the bench-work, wiring, and ballasting, I'm glad to be getting to this stage finally.   

[USMC0351]

Is it possable to put a thin layer of plaster over the Shapeways portal, enough to scratch some detail an age on it?

[GaryHinshaw]

I thought about that, but I decided it would be easier (and hopefully better looking) to cast them.  Thanks for the suggestion though.

[ednadolski]

Thin plaster would be pretty delicate, and likely would flake off from a plastic surface.

Ed

[Philip H]

Thin plaster would be pretty delicate, and likely would flake off from a plastic surface.

Ed

Which could make for an interesting long term weathering approach.

[USMC0351]

Wonder if the plastic could first be scuffed with steel wool or sandpaper? Just trying to think of something faster than building a mold.